In the copper electrolysis process conducted during copper smelting, impurities that are insoluble in the electrolyte are also generated as a residual by-product. This by-product contains significant quantities of platinum group elements such as Pt, Rh, Ir and Ru, as well as selenium, tellurium, gold, silver and copper. Many processes have already been proposed for separating and recovering these metals. For example, platinum group elements are recovered from the silver anode slime produced during a silver refining step, and from the slime generated by adding nitric acid to this slime, leaching out the metal components other than gold, and then reducing the residue. Conventionally, in order to dissolve these slimes, dissolution in aqua regia, dissolution in hydrochloric acid and hydrogen peroxide, or dissolution in hydrochloric acid under a stream of chlorine gas is conducted.
However, in the case of a material containing selenium/tellurium and platinum group elements, in which selenium and/or tellurium coexist with the platinum group elements, if reduction is used to generate a precipitate, then the platinum group elements form compounds with the selenium/tellurium, which are then very difficult to dissolve in aqua regia, or hydrochloric acid and hydrogen peroxide, meaning separation and recovery becomes impossible. Hydrogen peroxide decomposes on the surface of selenides, and is consequently effectively unable to function as an oxidizing agent. Furthermore, a process for roasting these compounds to effect a vapor state separation of selenium oxide and tellurium oxide has also been proposed, although the toxicity of these materials leads to significant environmental problems.
A process for separating platinum group elements and selenium/tellurium contained in a post-gold extraction liquid generated from a copper electrolysis slime, in which the chlorine ion concentration in the liquid is maintained at no more than 1.5 mol/L, while sulfur dioxide gas with a concentration of 8 to 12% is bubbled through the liquid at a temperature of 60 to 90° C., thus reducing and precipitating the platinum group elements (Japanese Unexamined Patent Application, First Publication No. 2001-316735), and a process for obtaining the extraction residue produced by solvent extraction of gold and platinum group elements from the hydrochloric acid leachate obtained from a copper electrolysis slime, and then introducing sulfur dioxide to the post-extraction liquid to reduce and precipitate the selenium/tellurium (Japanese Patent No. 3,087,758, and Japanese Unexamined Patent Application, First Publication No. 2001-207223) are already known.
However, in these processes, because a large number of parameters must be controlled during the selenium reduction, such as the hydrochloric acid concentration, the temperature, the sulfur dioxide gas concentration, and the sulfur dioxide gas flow rate, control of the process is difficult, leading to a reduction in the recovery rates for the platinum group elements and selenium/tellurium. In addition, managing the steps in the two-stage reduction treatment using sulfur dioxide is extremely difficult, and some incorporation of selenium/tellurium or platinum group elements in the precipitates is unavoidable, meaning separation that relies solely on sulfur dioxide reduction is unsatisfactory. Furthermore, separating platinum group elements and selenium/tellurium using solvent extraction is an expensive process, and the recovery treatment required following the extraction is both complex and time-consuming.
A process in which, instead of using treatment with hydrochloric acid and sulfur dioxide, the copper electrolysis slime is subjected to a leaching treatment in a sulfuric acidic solution under pressurized oxygen-enriched gas (Japanese Unexamined Patent Application, First Publication No. Hei 5-311258), and a process in which, following leaching of the copper electrolysis slime in a sulfuric acidic solution under pressurized oxygen-enriched gas, the leachate is desilvered by treatment with chlorine ions and a sodium thiosulfate solution, and copper is then added (Japanese Unexamined Patent Application, First Publication No. Hei 5-311264) have also been proposed. However, these types of processes that use copper under conditions of pressurized, oxygen-enriched gas are difficult to manage and very costly, and are consequently impractical.
Other known processes include a process in which an oxidizing agent is used to oxidize metallic selenium, and the resulting product is then neutralized with an alkali metal carbonate or hydroxide, thus forming an alkali metal selenate (Japanese Unexamined Patent Application, First Publication No. Sho 60-176908), a process in which a selenium-containing material is reacted with an alkali metal carbonate to generate an aqueous slurry, and this slurry is then baked in an oxidizing atmosphere to produce pellets, which are then subjected to water leaching (Japanese Unexamined Patent Application, First Publication No. Sho 56-5306), a process in which a tellurium-containing slime is dissolved in a mineral acid in the presence of an oxidizing agent, an alkali is then added to the solution to precipitate and separate the copper, and the remaining solution is then neutralized to precipitate out the tellurium (Japanese Unexamined Patent Application, First Publication No. Sho 56-84428), and a process in which a raw material such as a copper electrolysis slime is treated with a strong acid such as hydrochloric acid, and also with an oxidizing agent such as chlorine if the raw material includes compounds, and butyl carbitol is then used as the solvent for extracting tellurium (Japanese Unexamined Patent Application, First Publication No. 2000-239753). However, all of these processes have a large number of steps, and the recovery rates for selenium/tellurium are also low.
The present invention solves the above problems associated with the conventional technology, and has an object of providing a separation process which enables selenium/tellurium and platinum group elements to be easily and efficiently separated from a material containing selenium/tellurium and platinum group elements.
Furthermore, as described above, when a separation process that relies on vaporization by roasting is applied to selenium, a large proportion of the selenium becomes hexavalent, which places a large load on the subsequent waste water treatment.
Accordingly, the present invention provides a process for dissolving a material that contains both platinum group elements and selenium, which is capable of resolving the above problems associated with conventional processes, by providing a dissolution separation process that enables efficient leaching of selenium, thus enabling separation from platinum group elements.
In addition, as described above, managing the steps in a two-stage reduction treatment using sulfur dioxide is extremely difficult, and some incorporation of selenium or platinum group elements in the precipitates is unavoidable, meaning separation that relies solely on sulfur dioxide reduction is unsatisfactory. Furthermore, processes in which platinum group elements are removed by solvent extraction, and subsequently separated from selenium and/or tellurium are expensive, and the recovery treatment required following the extraction is time-consuming. Moreover, each of these processes describes the separation of platinum group elements and selenium that already coexist within a solution, and do not relate to the dissolution of a process precipitate that contains platinum group elements and selenium and the like.
Each of the selenium and tellurium recovery processes described above is a process in which the selenium and/or tellurium is oxidized and solubilized, but none of these processes enables the separation of platinum group elements from selenium at the dissolving stage.
Furthermore, in the recovery of rhodium, which is one of the platinum group elements, rhodium is very susceptible to oxidation, forming a very insoluble rhodium oxide, and is consequently very difficult to dissolve. A process for separating rhodium from a precipitate that contains noble metals, in which the noble metal-containing precipitate is heated with a carbon based reducing agent, and the resulting reduction product is reacted with a sulfating agent, thus forming a rhodium sulfate is known (Japanese Unexamined Patent Application, First Publication No. Hei 5-125461), although this process suffers from low yields and the requirement for a high treatment temperature.
The present invention provides a solution treatment process for a material that contains both platinum group elements and selenium, which is capable of resolving the above problems associated with conventional processes, by providing a treatment process in which selenium is dissolved selectively and separated efficiently from platinum group elements, and the platinum group elements remaining in the solid fraction are then dissolved and recovered.
In addition to the processes described above, known tellurium recovery processes include a process in which an anode slime produced during the electrolytic refining of copper or nickel is subjected to a wet treatment to separate the insoluble silver compounds, which are subsequently leached with ammonia or the like to separate the silver, while the resulting residue that contains tellurium is leached with sodium carbonate (Japanese Unexamined Patent Application, First Publication No. 2001-11547), and a process in which the tellurium-containing filtrate generated during the solvent extraction of gold is reduced to precipitate the selenium, and the remaining filtrate is then returned to sulfuric acid pressurized leaching conditions for leaching into the decoppered leachate (Establishment of copper precipitate wet treatment technology, Journal of the Mining and Materials Processing Institute of Japan, Vol. 1116, p. 484, 2000). However, processes for recovering tellurium from insoluble silver compounds suffer from poor tellurium migration rates. Furthermore, in processes in which the tellurium-containing filtrate is returned to pressurized leaching, the leaching rate is unsatisfactory if the tellurium is in metal form, causing an undesirable increase in the holdup volume in the process.
The present invention resolves these problems associated with the conventional treatment processes, by providing a treatment process in which a mixture of selenium and tellurium is alloyed with copper, this alloy is subjected to copper electrolysis to recover electrolytic copper and generate a selenium and tellurium slime, and leaching of this copper electrolysis slime is then used to leach out the tellurium and separate the selenium, thus enabling the selenium and tellurium to be processed with good efficiency.
As described above, in the copper electrolysis process of a copper smelting process, impurities that are insoluble in the electrolyte are generated as a residual by-product. This by-product contains significant quantities of gold, silver, copper, platinum group elements such as Pt, Rh and Ru, as well as Se and Te. Many processes have already been proposed for separating and recovering these noble metals. For example, a decoppered slime can be subjected to chlorination leaching, with silver and lead being recovered from the resulting residue, and gold being recovered from the leachate by a solvent extraction process. The residual liquid following this gold extraction contains platinum group elements, as well as Se and Te. This post-gold extraction liquid is then subjected to a reduction treatment by introducing sulfur dioxide gas into the system, the initial selenium precipitate that first is subjected to distillation to recover high purity selenium, and the resulting distillation residue is subjected to alkali melt treatment to effect a separation into a selenium-containing leachate and a platinum group element-containing residue, whereas the tellurium that is precipitated by continuing the introduction of sulfur dioxide gas into the above residual liquid is subjected to alkali leaching treatment to effect a separation into a selenium/tellurium-containing leachate and a platinum group element-containing residue, and selenium and tellurium, and the platinum group elements are then recovered from this leachate and residue respectively.
In this type of noble metal recovery system, the gold recovery process has conventionally employed a known solvent extraction process that uses dibutyl carbitol (DBC) (Japanese Unexamined Patent Application, First Publication No. Sho 57-79135). A process in which an aqueous solution of oxalic acid is added to the extracted solution to reduce and precipitate the gold is also known (Japanese Unexamined Patent Application, First Publication No. 2001-316735). However, solvent extraction processes that use DBC typically leave approximately 0.3% of the solvent in the post-extraction liquid. This residual solvent can be separated by distillation, but the small quantity of gold contained in the solvent remains, and a process for efficiently removing this gold during the subsequent steps is much sought after.
Furthermore, a process in which oxalic acid is added to the chlorination leachate from a copper electrolysis slime, and the resulting precipitate is treated with nitric acid and melted by heating (Japanese Examined Patent Application, Second Publication No. Sho 64-3930), and a process in which bis(2-butoxyethyl)ether is mixed with the chlorination leachate from a copper electrolysis slime, the gold is extracted into the organic phase by adding ether, this organic phase is scrubbed with hydrochloric acid, and then oxalic acid is added to reduce gold (Japanese Patent No. 3,087,758) are also known. However, processes in which gold is selectively reduced using oxalic acid suffer from extremely slow reaction rates in those cases where the chloride ion concentration of the chlorination leachate from the copper electrolysis slime is high, making the gold reduction step practically impossible.
On the other hand, a process that uses hydroxylamine hydrochloride, nitrous acid, or sulfurous acid as the reducing agent for extracting gold from gold-containing materials is also known (Japanese Unexamined Patent Application, First Publication No. Hei 2-97626). Furthermore, a process in which an alkylhydroxylamine is used as a complexing agent during the electroplating of palladium and gold and the like has also been disclosed (Japanese Unexamined Patent Application, First Publication No. Hei 2-221392). However, the quantity of gold remaining within the post-gold extraction liquid generated from a decoppered slime is minimal, and the quantities of selenium, tellurium, and platinum group elements are higher, and consequently even if hydroxylamine hydrochloride or an alkylhydroxylamine is added directly to this post-gold extraction liquid, an efficient recovery of gold is impossible.
The present invention seeks to overcome the above problems associated with conventional processes for recovering gold from a material containing selenium/tellurium and platinum group elements generated by treatment of the chlorination leachate from a copper electrolysis slime, by providing a process that enables the efficient separation and recovery of gold contained within such a material containing selenium/tellurium and platinum group elements.